Did you logged in the Db as administrator ?

This error does not appear with administrator user

Then log in as admin, then check Settings-> User -> Select the Corresponding user , open the user. Then check whether the user is manger in Purchase ? of course it will be user in Purchase.

the user is manager in Purchases already but does it has any relate to report ?

So we have to either make the user as manager in purchase or we have to set access right for the Purchase user. For setting Access right for purchase user,

Settings-> Database Structures ->Models , select the model project.forecast .Click on Edit . Then click on access rights.Click on add an item. Search purchase/user and select it.Give permission for the read and write.

sorry, relate to forecast

It's not working

It is the model in the custom module right ?

no, it 's a model from module project_forecast : a module of odoo enterprise